runner.arch returns lowercase 'arm64' instead of 'ARM64' when using -self-hosted on ARM64 hosts

Bug report info

act version:            0.2.89
GOOS:                   darwin
GOARCH:                 arm64
NumCPU:                 18
Docker host:            unix:///var/folders/lb/xscfg2ss0jj8gwmxp7zl8s000000gn/T/podman/podman-machine-default-api.sock
Sockets found:
	/var/run/docker.sock(broken)
Config files:           
	/Users/pealmeid/Library/Application Support/act/actrc:
		-P ubuntu-latest=catthehacker/ubuntu:act-latest
		-P ubuntu-22.04=catthehacker/ubuntu:act-22.04
		-P ubuntu-20.04=catthehacker/ubuntu:act-20.04
		-P ubuntu-18.04=catthehacker/ubuntu:act-18.04
Build info:
	Go version:            go1.26.3
	Module path:           command-line-arguments
	Main version:          
	Main path:             
	Main checksum:         
	Build settings:
		-buildmode:           exe
		-compiler:            gc
		-ldflags:             -X main.version=0.2.89
		DefaultGODEBUG:       cryptocustomrand=1,tlssecpmlkem=0,urlstrictcolons=0
		CGO_ENABLED:          1
		CGO_CFLAGS:           
		CGO_CPPFLAGS:         
		CGO_CXXFLAGS:         
		CGO_LDFLAGS:          
		GOARCH:               arm64
		GOOS:                 darwin
		GOARM64:              v8.0
Docker Engine:
	Engine version:        5.8.6
	Engine runtime:        crun
	Cgroup version:        2
	Cgroup driver:         systemd
	Storage driver:        overlay
	Registry URI:          
	OS:                    fedora
	OS type:               linux
	OS version:            44
	OS arch:               arm64
	OS kernel:             7.1.4-200.fc44.aarch64
	OS CPU:                9
	OS memory:             7904 MB
	Security options:
		name=seccomp,profile=default
		name=rootless
		name=selinux

Command used with act

act push -P ubuntu-latest=-self-hosted

Describe issue

When running act with -P ubuntu-latest=-self-hosted on an ARM64 host (macOS or Linux), RUNNER_ARCH and runner.arch are set to arm64 (lowercase) instead of ARM64.

The GitHub Actions spec (https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/accessing-contextual-information-about-workflow-runs#runner-context) defines the only valid values for runner.arch as X86, X64, ARM, ARM64 - all uppercase. Receiving arm64 breaks workflows that compare against the spec values, e.g. if: runner.arch == 'ARM64'.

Root cause: goArchToActionArch() in pkg/container/host_environment.go maps "aarch64" -> "ARM64" but is missing "arm64", which is what Go's runtime.GOARCH returns on ARM64 hosts. The value falls through the mapper and is returned verbatim in lowercase. The Docker container path (docker_run.go) already handles "arm64" correctly.

Expected: RUNNER_ARCH=ARM64 Actual: RUNNER_ARCH=arm64

Link to GitHub repository

No response

Workflow content

name: Check Runner Arch
on: [push]
jobs:
  check-arch:
    runs-on: ubuntu-latest
    steps:
      - name: Print RUNNER_ARCH env var
        run: echo "RUNNER_ARCH=$RUNNER_ARCH"
      - name: Print runner.arch context
        run: echo "runner.arch=${{ runner.arch }}"

Relevant log output

# Running: act push -P ubuntu-latest=-self-hosted
RUNNER_ARCH=arm64
runner.arch=arm64
# Expected: ARM64

Additional information

No response